Electron Attachment to C₇F₁₄, Thermal Detachment from C₇F₁₄^–, the Electron Affinity of C₇F₁₄, and Neutralization of C₇F₁₄^– by Ar⁺

Abstract

Rate coefficients and branching fractions have been measured for electron attachment to perfluoromethylcyclohexane, C(7)F(14), along with thermal detachment rate coefficients for C(7)F(14)(-), from 300 to 630 K, using a flowing-afterglow Langmuir-probe apparatus. The attachment rate coefficient at room temperature is 4.5 ± 1.2 × 10(-8) cm(3) s(-1) and increases with temperature at a rate described by an activation energy of 50 ± 25 meV. Thermal electron detachment is negligible at room temperature, but measurable at 600 K and above, reaching 2300 ± 1300 s(-1) at 630 K. Analysis of the attachment-detachment equilibrium yields EA(C(7)F(14)) = 1.02 ± 0.06 eV, in agreement with the literature value while more than halving the uncertainty. Implications of the measurement for the electron affinity of SF(6) are discussed. The dominant product of electron attachment is the parent anion, but C(6)F(11)(-) and C(7)F(13)(-) are also observed at very low levels (<0.1%) at room temperature and increase in importance as the temperature is increased, reaching ~10% each at 630 K. In the course of this work we have also measured rate coefficients for the neutralization of C(7)F(14)(-) by Ar(+) at 300, 400, and 500 K: 4.8, 3.5, and 3.1 × 10(-8) cm(3) s(-1), respectively, with uncertainties of ±5 × 10(-9) cm(3) s(-1).

Atmospheric pressure anion mass spectrometry: electron affinities and activation energies of thermal electron attachment – perfluoromethylcyclohexane, C7F14

“…Above 400K, the fragment ions increase and become the dominant ions in the 4.5 ms data by 630K. The parent negative ion intensity in the 4.5 ms data is over 99% at 600K and decreases to about 10% at 620K …”

“…Barrera demonstrated that the API-NIMS data was consistent with an AE a (C 7 F 14 ) of 1.06(10) eV. [10][11][12]16,17] Miller and co-workers determined the (flowing afterglow [19] ) FLAG-12, AE a (C 7 F 14 ), 1.02(6) eV, increasing the precision of the TCT [16] and ECD values. [19] In 1991, Mock and Grimsrud reported photodetachment onsets of C 7 F 14 and SF 6 anions at atmospheric pressure, 3.3 eV, consistent with the 1979 study of electron attachment at 3500K indicating equal gs-AE a (C 7 F 14 ) and gs-AE a (SF 6 ).…”

“…Miller and co‐workers reported the AE a (C 7 F 14 ) 1.02(6) from the detachment rate constants 7 s –1 at 500K and 2300 s –1 at 630K. The C 7 F 13 and C 6 F 11 anions were less than 0.1% of the total anions from 300 to 400K and increased from 400 to 630K where the c‐C 6 F 11 anion and the C 7 F 13 anion were 50% and 20% of the total anion ion intensity at 4.5 ms . By contrast, Grimsrud observed the anion ratio of [C 7 F 14 /C 7 F 13 ] = 9 up to 553K in agreement with the ratio of [C 7 F 14 /C 7 F 13 ] = 8.5/1.5 up to 563K reported in the dissertation by Shuie …”

“…[1,[10][11][12][13][14] The primary purpose of this paper is to place these results in the literature and update the comparisons to reduce the uncertainty in the kinetics and thermodynamics of thermal electron attachment to C 7 F 14 . [1][2][3][4][5][8][9][10][11][12][15][16][17][18][19][20][21][22][23] In 1984, Alge and co-workers measured the k 1 (C 7 F 14 ) from 200 to 600K using a (flowing afterglow [15] ) FLAG-84 mass spectrometer technique. The upper limit of 300 amu precluded observation of C 7 F 14 (350 amu) and C 7 F 13 (331 amu).…”

“…[10][11][12]16,17] Miller and co-workers determined the (flowing afterglow [19] ) FLAG-12, AE a (C 7 F 14 ), 1.02(6) eV, increasing the precision of the TCT [16] and ECD values. [19] In 1991, Mock and Grimsrud reported photodetachment onsets of C 7 F 14 and SF 6 anions at atmospheric pressure, 3.3 eV, consistent with the 1979 study of electron attachment at 3500K indicating equal gs-AE a (C 7 F 14 ) and gs-AE a (SF 6 ). [18,23] Since 2000, a range of lifetimes of C 7 F 14 anions observed in alkali metal beam studies and magnetized Q machine plasma at 0.2 eV suggest multiple positive AE a (C 7 F 14 ).…”